In the fabrication of electronic devices, one of the most critical and crucial steps is the lithographic processing for providing desired patterns such as circuit patterns and vias to connect different layers to each other.
Traditionally, wet etching processes have been employed to define the desired pattern. For instance, a resist material is typically exposed to actinic radiation such as ultraviolet light, electrons beams or x-rays in the desired pattern. The exposed regions in the case of a positive resist and the unexposed regions in the case of a negative resist are then removed or developed by dissolving in a suitable solution. After the development, the desired pattern remains in the resist layer. Next, an additional processing step such as etching is used to transfer the resist pattern into one of the functional layers of the electronic device. The resist layer is then removed.
However, in an attempt to eliminate the development step and/or pattern transfer step, suggestions have been made to employ dry etching techniques. One such technique employs ablative decomposition using high powered pulsed sources of irradiation as disclosed in U.S. Pat. No. 4,414,059, disclosure of which is incoporated herein by reference. In that process, a large number of photons of particular wavelength are directed to the patternable material in a short time. This results in breaking the polymer chain of the patternable material into fragments which ablate and are blown off as volatile by-products. Such processes typically employ wavelengths of between about 190 nanometers and about 450 nanometers. Ablative decomposition can also be used to directly etch a pattern into a functional layer of an electronic device, eliminating the need for the photoresist step.
The masks employed for such purposes must withstand peak laser fluxes of about 500 mj/cm.sup.2 -pulse without damage. Presently, one such mask employed is described in U.S. patent applications Ser. Nos. 924,480 and 341,273 to Lankard, et al. Such masks are fabricated by etching the desired pattern into a reflecting thin film multilayer containing about 10 to about 30 layers. Such films are adequate to withstand the required laser irradiation. However, such are relatively difficult to etch and the yields are relatively low. Accordingly, it would be desirable to provide ablation masks whereby the technique is relatively easy to perform and the yields are relatively high.